The Effects of Various Factors on Plant Yield.
Yield of commercially valuable species in the natural environment may be suboptimal as plants often grow under unfavorable conditions, such as at an inappropriate temperature or with a limited supply of soil nutrients, light, or water availability. Various factors that may affect yield, crop quality, appearance, or overall plant health include:
Nutrient Limitation
Nitrogen (N) and phosphorus (P) are critical limiting nutrients for plants. Phosphorus is second only to nitrogen in its importance as a macronutrient for plant growth and to its impact on crop yield.
Nitrogen and carbon metabolism are tightly linked in almost every biochemical pathway in the plant. Carbon metabolites regulate genes involved in nitrogen acquisition and metabolism, and are known to affect germination and the expression of photosynthetic genes (Coruzzi et al., 2001) and hence growth. Gene regulation by C/N (carbon-nitrogen balance) status has been demonstrated for a number of nitrogen-metabolic genes (Stitt, 1999); Coruzzi et al., 2001). A plant with altered C/N sensing may exhibit improved germination and/or growth under nitrogen-limiting conditions.
Increased tolerance to abiotic stresses, such as water deprivation, salt, freezing and other hyperosmotic stresses, and cold, and heat, may improve germination, early establishment of developing seedlings, and plant development.
In water-limited environments, crop yield is a function of water use, water use efficiency (WUE; defined as aerial biomass yield/water use) and the harvest index (HI; the ratio of yield biomass to the total cumulative biomass at harvest). WUE is a complex trait that involves water and CO2 uptake, transport and exchange at the leaf surface (transpiration). Improved WUE has been proposed as a criterion for yield improvement under drought. Water deficit can also have adverse effects in the form of increased susceptibility to disease and pests, reduced plant growth and reproductive failure. Genes that improve WUE and tolerance to water deficit thus promote plant growth, fertility, and disease resistance. Enhanced tolerance to these stresses would lead to yield increases in conventional varieties and reduce yield variation in hybrid varieties. Altering the timing of flowering can also enhance the ability to a plant to maintain yield under water limited conditions. For example, acceleration of flowering and maturation may allow a plant to set seed earlier in the growing season and thereby avoid severe water limitation which occurs late in the season.
Plant pathogen injury may affect any part of a plant, and include defoliation, chlorosis, stunting, lesions, loss of photosynthesis, distortions, necrosis, and death. All of these symptoms ultimately result in yield loss in commercially valuable species.
Fortunately, a plant's traits, including its biochemical, developmental, or phenotypic characteristics that enhance yield or tolerance to various abiotic or biotic stresses, may be controlled through a number of cellular processes. One important way to manipulate that control is through transcription factors—proteins that influence the expression of a particular gene or sets of genes. Transformed and transgenic plants that comprise cells having altered levels of at least one selected transcription factor, for example, possess advantageous or desirable traits. Strategies for manipulating traits by altering a plant cell's transcription factor content can therefore result in plants and crops with commercially valuable properties. We have identified polynucleotides encoding transcription factors, including G1760 and closely-related sequences, developed numerous transformed or transgenic plant lines using these polynucleotides, and analyzed the plants for improved traits, such as altered C/N sensing, water or nutrient use efficiency, tolerance to abiotic stresses, such as water deprivation, cold, heat, low nitrogen conditions, and/or resistance to disease. In so doing, we have identified important polynucleotide and polypeptide sequences for producing commercially valuable plants and crops as well as the methods for making them and using them. Other aspects and embodiments of the invention are described below and can be derived from the teachings of this disclosure as a whole.